chap, ii.] of Plants. Treviranus and Meyen. 521 



ill-luck constantly overlooks what is valuable in itself and 

 important in its results, Meyen generally picks out the best 

 things from the books before him; Treviranus timidly avoids 

 expressing any view decidedly and maintaining it ; Meyen, amid 

 the multiplicity of the labours which we have already described, 

 finds no time to arrange his thoughts, is hasty in judgment 

 and often contradicts himself. But with all these defects, he 

 is still the champion of the new tendencies that were being 

 developed, while Treviranus lives entirely in the past, and 

 shows no trace of the actively creative spirit which was soon to 

 burst forth so mightily in every branch of natural science. 



If we examine what both these writers have said on the 

 subject of the nutrition of plants, we shall find that the differ- 

 ence in their general views in physiology as described above 

 appears at once in their treatment of the work of suction in 

 the roots, and of the means by which the sap ascends ; here in 

 Treviranus the vital force is everything ; it makes the vessels 

 of the wood conduct the juices from the roots into the leaves, 

 with other antiquated notions of the kind; Meyen on the 

 contrary adopts Dutrochet's position, and even rejects De 

 Candolle's spongioles. Treviranus knows not what to make of 

 respiration ; Meyen explains it without hesitation as a function 

 that answers to respiration in animals, and finds in it the main 

 cause of the natural heat which Treviranus derives in the old 

 mystical fashion from the vital force. In one point however 

 they agree, namely, in a complete misconception of the con- 

 nection between the decomposition of carbon dioxide in the 

 leaves and the general nutrition of the plant. It is necessary 

 to the understanding of the confusion of ideas which had crept 

 at this time into the doctrine of nutrition, and to a right estimate 

 of the services of Liebig and Boussingault on this point, that 

 we should look a little more closely into the chemical part of 

 the theory of nutrition in Treviranus and Meyen. 



Treviranus in the introduction to his book repudiated the 

 idea of a vital force separable from matter, but he was in fact 



